I'm a little confused by the custom block number, string and boolean inputs. Can someone be so kind as to explain them to me? I just don't get what they do/how to set them.

These blocks are parameters to your block/function. Based on the datatype you choose (ie: number, string, or boolean) it tells your custom block what kinds of objects you expect to drop into the your custom block.
For example say you use the <move steps> block in the motion category and the <say > block from looks. as part of your custom block. Then you would use two parameters one a number and one a string. You would then click on the “number1” in the custom block and drag it into the number “area” of the <move steps> block. You could also drag the “string1” in the custom block and drag it into the string area of the "say “ block.

Notice I said ”what kinds of objects you expect to drop in“ not ”can drop in“. Since a variable can be a number or a string, you could create a custom block which expects a number but the variable you pass is a string (which the interface allows) and thus wind up with a case where you ask a sprite to ”Move steps". It doesn't complain when this executes, which is interesting, and it doesn't move either.

There is also an explanation of the customized blocks (Make a Blocks) on this page– some cosmetic details have changed, but the basic concepts are there:
http://mv.ezproxy.com.ezproxyberklee.flo.org/prototype#make-blocks

mrsteve
It doesn't complain when this executes, which is interesting, and it doesn't move either.

That's because it treats the string as numerical value 0.

Exactly. See http://mv.ezproxy.com.ezproxyberklee.flo.org/wiki/Casting.

@Steve: They are basically arguments to your function. You add an input, and it shows up as a text box in the block, like the (10) in Move (10) steps.